Tissue fusion has been used in medical procedures for many decades, primarily to prevent bleeding from severed blood vessels. One age-old technique of fusing tissue involves heat application to cauterize vessels. More recent techniques involve the application of electrosurgical electrical energy to tissue to create the heat necessary for tissue fusion. The electrical energy may be applied in a coagulative or a coaptive manner.
Coagulative tissue fusion involves applying electrosurgical energy to the open vessel. The heat created by the electrical energy shrinks and constricts the blood vessel, and blood coagulation contributes to occluding the vessel. Generally speaking, coagulative tissue fusion is primarily useful on relatively small vessels. In electrosurgery, coagulative tissue fusion occurs during standard coagulation and spray coagulation. Coagulative tissue fusion on larger vessels is regarded as less reliable, and therefore poses more risks of internal bleeding after the surgery has been completed. For this and other reasons, coaptive electrosurgical tissue fusion, or some other type of tissue sealing and closure technique, such as mechanical ligature, is generally regarded as more favorable and reliable for larger vessels.
Coaptive electrosurgical tissue fusion involves physical apposition and compression of the tissue which surrounds the lumen, duct, passageway or chamber to be sealed, followed by heating the compressed apposed tissue portions. Usually the source of heat is electrical energy, which is either conducted through the tissue or is conducted through a heating element that is placed in contact with the tissue. One well-known and relatively old technique of coaptive electrosurgical tissue fusion involves grasping the vessel with a hemostat (a scissors-like clamping device) and conducting electrosurgical energy through the hemostat to the tissue. More recent coaptive electrosurgical tissue fusion devices use a specifically-configured handpiece with jaws that clamp around and compress the vessel while a controlled and regulated amount of electrical current is applied to electrodes within the jaws to heat the tissue. Radio frequency (RF) energy is used primarily to create the heating effects because the tissue conducts the current, and RF currents minimally stimulate the nervous system, if at all. Other known sources of heating energy include direct current (DC) applied to resistive heating elements, ultrasound which vibrates the tissue to generate heat, microwaves which interact with the molecular structure of the tissue to generate heat, and light which transfers energy to the cellular components of the tissue, among others.
In coaptive tissue fusion, it is very important to control the amount of energy delivered to the tissue to achieve an effective seal or fusion of the tissue. An effective seal is one which prevents leaks caused by blood pressure and other stresses and pressures from the fluid within the occluded lumen, duct, passageway or chamber. Applying too much energy to the tissue may destroy or denature the tissue to the point where collagen and elastin fibers within the tissue are incapable of fusing and intertwining in such a way to achieve an effective seal. Intertwining and fusing the fibers within the tissue of the two apposite tissue portions is believed to be the primary mechanism for fusing and sealing the tissue. Applying too much energy may obliterate the tissue or destroy or compromise the ability of the fibers to loosen and unwind and thereafter tangle, intertwine and fuse to join the previously separate opposed tissues in a single tissue mass. Applying too little energy to the tissue will not increase the flexibility of the fibers to the point where they will loosen enough to interact and fuse sufficiently with the fibers of the apposite tissue.
In those prior art tissue sealing devices such as the hemostat, the application of the electrical energy to the tissue is not specifically controlled but is instead left to the surgeon to determine when enough heat has been applied. Determining when enough heat energy has been applied is particularly difficult if not impossible, because different tissues respond differently. Determining whether a seal is effective by simple observation is impossible. Therefore, most modern coaptive tissue sealing devices attempt to control the application of energy automatically to achieve an effective seal.
Modern coaptive tissue sealing devices typically use complex functional components for measuring and calculating tissue impedance, tissue temperature and other physical tissue parameters to determine and control the amount of energy applied. Most of these devices include feedback control loops which depend on the values of these tissue parameters to adjust the energy delivered to the tissue. In most cases, these tissue parameters are calculated based on measurements of the voltage and current applied to the tissue. Calculations based on the measurements of the voltage and current must thereafter be performed, and the calculated values used in the feedback control loops and other power delivery functionality of the devices. The capability of such prior art tissue sealing devices is therefore subject to a number of complex constraints, including the accuracy of sensing the values and the tissue parameters, the speed and reliability of making the calculations, and the ability of the components of the device to respond. Consequently, most modern coaptive tissue sealing devices are relatively complex in their functionality and relatively expensive because of their complex functionality.
Examples of these types of prior art tissue sealing devices are those which respond to a measured, fixed or variable impedance level occurring while heating the tissue to indicate that the seal is complete. Upon achieving this impedance level, the delivery of electrical energy to the tissue is terminated. Detecting impedance can be computationally intensive and time consuming, thereby delaying the calculated value of the tissue impedance relative to the actual value of the tissue impedance at the time that the calculation is made available. Detecting impedance can be virtually impossible under conditions where the electrical energy is arcing between the jaws which grasp the tissue. Arcing at the ending stages of the tissue sealing process is prevalent in prior art RF tissue sealing devices. Consequently, using an impedance value to establish the point for terminating the delivery of RF electrical energy to the tissue makes it very difficult or impossible to achieve optimum sealing conditions.
Other types of prior art tissue sealing devices determine the impedance level while modulating the electrical energy delivered to the tissue. Modulating the electrical energy delivered is intended to prevent overheating of the tissue, and in that sense is an implicit recognition of the slow response of the feedback control system in regulating the output energy delivered to the tissue. Moreover, modulating the electrical energy delivered while simultaneously calculating impedance and other control parameters increases the complexity of the equipment required.
Still other types of prior art tissue sealing devices automatically reduce the electrosurgical power delivered throughout the tissue sealing event to reduce tissue charring, and then terminate the energy delivery when the current drops below a certain level. Reducing the energy delivery rate extends the time required to achieve an adequate seal, and may therefore result in greater thermal damage to the tissue because of the prolonged heat application time.
Because of the variable and uncertain effects from most prior art tissue sealing devices, surgeons are frequently prone to perform multiple seals on the same vessel in an attempt to assure that one of these seals will be effective. Performing multiple seals on the same vessel is time-consuming. The number of seals necessary to be performed in a surgical operation can vary according to the type of operation, but the use of a tissue sealing device in surgery usually occurs under circumstances where the surgeon has judged that the procedure will be more efficiently performed by using a tissue sealing device compared to using an alternative tissue sealing technique such as mechanical ligature. Accordingly and in addition to the requirement for permanent and leak-free seals, the speed at which the tissue sealing device accomplishes the seal is very important. Minimizing the time required to achieve effective seals diminishes the time of the surgical procedure and therefore minimizes risks associated with the procedure.